Biomechanical Responses and Functional Outcomes in Large Animal and Human Surrogate Models of Primary Blast Injury

Abstract

The growing use of explosive weapons over the past century has led to a rise in blast traumatic brain injuries (bTBIs), particularly among military personnel. More than 515,000 servicemembers have been diagnosed with a traumatic brain injury (TBI) since the year 2000, and blast was reported to be the most common cause of TBI in modern U.S. military conflicts, comprising 33.1% of reported cases ((Lindquist et al., 2017; Traumatic Brain Injury Center of Excellence (TBICoE), 2025). Conflicts between Ukraine and Russia continue to highlight the enduring and serious risk of bTBI affecting both military forces and civilian populations (Lawry et al., 2025). These injuries are frequently associated with a wide range of physical, cognitive, behavioral, and psychological symptoms, such as headaches, dizziness, impulsivity, sleep disturbances, memory deficits, anxiety, depression, and mood alterations, which can significantly interfere with daily activities. However, the injury mechanisms causing these functional impairments remain poorly understood. The high incidence and impact of bTBI has brought increased attention to the effectiveness of combat helmets in mitigating blast injury, as current infantry combat helmets were not designed for protection against primary blast. Previous computational and experimental findings have suggested that during a blast exposure, the shock wave infiltrates the gap between the head and helmet and generates regions of increased pressure that are orientation-dependent (Mott et al., 2008; Thomas and Johnson, 2024). The overall objective of this study was to improve the understanding of bTBI biomechanics by evaluating the protective effectiveness of a combat helmet in mitigating blast loading and associated injury outcomes. The influence of blast orientation on functional outcomes was also evaluated at an acute timepoint. Using an instrumented human surrogate model, the effect of blast intensity, orientation, and the presence of a combat helmet on blast loading was examined. In a frontal blast orientation, peak pressures were shown to be reduced at the forehead and front of the head but increased at the back of the head with the combat helmet. When the headform was rotated 45 degrees about the transverse axis, peak pressures and total impulses were notably increased at all measured locations on the head with the addition of the combat helmet, highlighting the need for protective equipment that prevents this increased loading on the head surface. The effect of this increased pressure on injury response was evaluated in a clinically-relevant pig model of bTBI. Findings from this study suggested that the blast exposure group exhibited greater motivation and interest in rewards than the sham group, which could be an indication of impulsive or risk-taking behaviors. The effects of blast orientation on affective behavior and memory and cognition were also evaluated in a translational preclinical model. The frontal blast group expressed primarily increased motivation and interest in rewards compared to sham, which is suggestive of impulsivity, while the lateral blast group primarily exhibited decreased approach behaviors relative to sham, which could be indicative of anhedonia, or a reduced ability to experience pleasure. This work demonstrated that orientation, blast intensity, and the presence of the combat helmet each influenced the blast dynamics and loading on the surface of the head and offered preliminary, yet meaningful, insights into the effects of orientation and the combat helmet on injury outcomes after blast exposure.